The Rogue

Signaling for her companions to wait, a halfling creeps forward through the dungeon hall. She presses an ear to the door, then pulls out a set of tools and picks the lock in the blink of an eye. Then she disappears into the shadows as her fighter friend moves forward to kick the door open.
A human lurks in the shadows of an alley while his accomplice prepares for her part in the ambush. When their target — a notorious slaver — passes the alleyway, the accomplice cries out, the slaver comes to investigate, and the assassin’s blade cuts his throat before he can make a sound.
Suppressing a giggle, a gnome waggles her fingers and magically lifts the key ring from the guard’s belt. In a moment, the keys are in her hand, the cell door is open, and she and her companions are free to make their escape.
Rogues rely on skill, stealth, and their foes’ vulnerabilities to get the upper hand in any situation. They have a knack for finding the solution to just about any problem, demonstrating a resourcefulness and versatility that is the cornerstone of any successful adventuring party.

In The Nameless Trilogy World

In the modern, urban setting of The Nameless Trilogy, the rogue thrives. Plenty of people to cheat, plenty of schemes to get up to, plenty of thieves to help, plenty of places to hide when the police see you. It is therefore no wonder why so many people in the city, when looking for an adventurer to do a job, will usually turn to the rogue. The rogue does not confront threats head-on usually, choosing instead to stick to the shadows and attack when least expected. The thieves' guilds of the cities will always employ rogues who can pick locks, keep a look out, or take out guards from behind without being seen.
Beyond the city, the usefulness of the rogue continues. With stealth to match that of rangers, and an eye for detail rivaling that of wizards, the rogue instantly becomes a useful hunter when sent on a mission beyond the city. Rogues usually possess many skills, all of which they use in their daily rigorous jobs.
When considering a rogue, you have access to many options and many skill sets. In terms of world building, there is not much I have to inform you of. Rather, consider your character. Are they part of a thieve's guild or mercenary company? Do they do jobs in the city or in the country? If placed in an unusual environment, what skills or knowledge do they possess that they could use to escape that strange place?
While it is typical for a rogue to have a mysterious or painful background, how would this or perhaps other non-traditional backgrounds influence your character? Are they on a journey of redemption or are they trying to achieve some end goal?

Resources:

• Player's Handbook
• Xanathar's Guide to Everything
• Xanathar's Lost Notes to Everything Else

Subclasses:

• Thief (PHB)
• Assassin (PHB)
• Arcane Trickster (PHB)
• Inquisitive (XGtE)
• Mastermind (XGtE)
• Scout (XGtE)
• Swashbuckler (XGtE)
• Divine Herald (XLNtEE)